Abstract: Endothelial biomechanics is increasingly recognized to play a key role in multiple endothelial functions. Our studies focus on regulation of endothelial biomechanics by oxidized lipids, which we showed to induce significant endothelial stiffening. Our long term goal is to elucidate the mechanisms responsible for dyslipidemia-induced changes in endothelial biomechanics and to determine the contribution of these mechanisms to endothelial dysfunction. During the current funding period of this grant, we provided significant mechanistic insights into dyslipidemia-induced stiffening of aortic endothelial cells (EC) showing that it critically depends on CD36 scavenger receptor and activation of RhoA/ROCK cascade. We also discovered that oxLDL/dyslipidemia and pro-atherogenic disturbed flow (DF) environment have a synergistic effect in inducing EC stiffening in vitro and in vivo. In the current proposal, we extend these studies to address three new goals: In Aim 1, we focus on elucidating further the mechanism of oxLDL-induced EC stiffening. First (aim 1A), we will determine whether the role of CD36 in EC stiffening is to provide the route for oxLDL internalization with subsequent incorporation of oxidized lipids into the membrane or whether CD36 is required to induce a signaling cascade that leads to EC stiffening. We will also determine the impact of fatty acids known to bind to CD36 on EC stiffness. In the second part of the aim (1B), we will investigate the mechanistic link between CD36 mediated oxLDL uptake and activation of the RhoA cascade, which based on our preliminary data, we propose to be mediated by the dissociation of RhoA from the inhibitory regulator GDI-1. In Aim 2, we focus on the role of oxLDL/DF-induced EC stiffening in the disruption of the endothelial barrier and endothelial-monocyte adhesion (aim 2B). First (aim 2A), we are proposing to investigate in depth the synergistic impact of oxLDL and DF on the activation of the RhoA/ROCK cascade and to discriminate between the contributions of RhoA-dependent EC stiffening vs. apoptosis in the disruption of the EC barrier. In the second part of the aim (2B), we investigate the role of oxLDL-induced EC stiffening in monocyte adhesion by discriminating between the impacts of EC stiffening vs. oxLDL-induced activation of the inflammatory NFkB cascade and increase in the expression of endothelial adhesion molecules. In Aim 3, these studies are extended to investigate the mechanism of dyslipidemia-induced endothelial stiffening in vivo and its contribution to the formation of atherosclerotic lesions. This goal will be achieved using two models of endothelial-specific CD36-deficient mice, a Ti2e- driven model, which is CD36-deficient from birth and VEcad-driven inducible model. Both models will be tested on the backgrounds of two major models of mouse dyslipidemia, ApoE-/- and LDLR-/-. Taken together, these new studies are expected to provide significant new insights into our understanding of endothelial biomechanical properties under dyslipidemic conditions particularly in pro-atherogenic hemodynamic environment.